Regular Wave Interaction with Elastic Floating Structures

Regular Wave Interaction with Elastic Floating Structures image

In this test case, floating flexible structures of varying dimensions are subjected to regular waves. The study aims to provide novel experimental data to assist with the development of a coupled numerical methodology for simulating fully nonlinear hydroelastic interactions with highly-flexible floating structures. The data was collected as part of the EPSRC project EP/N008847/1: ‘A zonal CFD approach for fully nonlinear simulations of two vessels in launch and recovery operations’.

Application Area

  • Offshore Engineering

Modelling Approach

  • Physical

Physics

Fluid Mechanics

Air/Gas phase dynamics
  • Still air/gas
Water/Fluid phase dynamics
  • Waves

Solid Mechanics

Geometry
  • Basic geometry
Material Properties
  • Elasticity
Body Motion
  • Restrained

Contributors

  • Scott Brown
  • Deborah Greaves
Contact person
Scott Brown
Mail Scott

Description

In this test case, floating flexible structures of varying dimensions are subjected to regular waves. The study aims to provide novel experimental data to assist with the development of a coupled numerical methodology for simulating fully nonlinear hydroelastic interactions with highly-flexible floating structures. The data was collected as part of the EPSRC project EP/N008847/1: ‘A zonal CFD approach for fully nonlinear simulations of two vessels in launch and recovery operations’.

Experimental Set-up

The experiments were performed in the COAST Laboratory at University of Plymouth, UK, using a wave and current flume that is 35m in length and 0.6m in width. The flume has a single piston-type, force feedback controlled wave paddle, and has an absorbing beach at the far end. The water depth was set to 0.75m.

Coordinate System

The coordinate system used throughout this document has been defined with: the z axis running vertically (positive z upwards) with the z = 0 corresponding to the still water level, and; the positive x axis running in the direction from the wave makers to the beach. The y axis is then defined according to the right-hand-rule. The origin is located at the centreline of the fixed edge of the structure.

Instrumentation

The structure’s deformation is tracked using a non-contact Qualisys motion capture system, providing the instantaneous position of fixed markers located on the top edge of each structure at a sampling rate of 128 Hz. The x-coordinate of these markers are provided in Table 2. To minimise reflection off the glass side walls and free surface, the infrared LED cameras are positioned at an angle above the open-topped wave flume, focusing on the top of the structure. The system is calibrated relative to a fixed point on the bottom of the flume, with a typical residual in the range of 0.5 − 1 mm. To record the free surface elevation four resistance wave gauges are installed (see Figure 2) at x = -3.6m (WG1); x = -2.6m (WG2); x = -0.1m; and x = 2m (WG4). Once calibrated, the wave gauges have an associated error of less than 0.36%.

Experimental Test Program

Four structures of varying dimensions are tested. Each structure is constructed from silicone sponge with elastic properties E = 5.65 x 105Pa and ν = 0.49. The density of each structure is approximately 380 kg/m3 but varies slightly between structures (see Table 2). Each structure is installed such that the upstream edge is constrained at the vertical equilibrium location, using a top mounted approach to minimise the influence on the hydrodynamics. The remainder of the structure is floating and free to deform (Figure 1). Each structure is subjected to regular waves with period T = 1.04s and height H = 0.018m.

Table 1: Dimensions and properties of each structure. Note that E is Youngs Modulus and ν is the Poisson Ratio.
Structure Length Width Height Density E ν
  [m] [m] [m] [kg/m3] [Pa] [-]
A 0.960 0.146 0.025 369 5.65 x 105 0.49
B 0.483 0.146 0.025 362 5.65 x 105 0.49
C 0.953 0.147 0.100 388 5.65 x 105 0.49
D 0.961 0.595 0.025 412 5.65 x 105 0.49
Table 2: Marker ID numbers and x-coordinate for each structure. The provided data is on the centreline (y=0) of each structure. All values are given in metres.
Structure Marker Number
  1 2 3 4 5 6 7 8 9
A 0.115 0.215 0.315 0.415 0.515 0.615 0.715 0.815 0.915
B 0.115 0.215 0.315 0.415 0.515 0.615 0.715 0.815 0.915
C 0.115 0.215 0.315 0.415 0.465 - - - -
D 0.115 0.215 0.315 0.415 0.515 0.615 0.715 0.815 0.915

Physical Measurement Data

The experimental data can be found at Brown et al. 2023 ( see 'Relevant References' below) and is provided in a separate text file for each case. The text files are arranged using the following conventions:

  • The text file “L&R_ElasticStructure.txt” contains time series data for the structural displacement data for structure , as well as the in-situ wave gauge data.
  • All of the data has been filtered using a 10th order low-pass Butterworth filter with a normalised cut-off frequency of 0.0469Hz;
  • The wave gauge and paddle displacement data has not been filtered;
  • The deflection data is provided relative to the equilibrium position of the structure;
  • The deflection and surface elevation data is provided in millimetres; time is in seconds;
  • The first and second row contains the column headers and units, respectively, and begin with a '%' for (MATLAB) post-processing purposes;
  • The order of the columns is as follows for Structures A, C and D:
    • time;
    • surface elevation at WG1 (in-situ);
    • surface elevation at WG2 (in-situ);
    • surface elevation at WG3 (in-situ);
    • surface elevation at WG4 (in-situ);
    • X deflection at Marker 1;
    • Z deflection at Marker 1;
    • X deflection at Marker 2;
    • Z deflection at Marker 2;
    • …
    • X deflection at Marker 9;
    • Z deflection at Marker 9;
  • The order of the columns for the data file for Structure B is the same as above but ends at Marker 5.

    • NOTE: When using this data please state that 'the physical data is from the CCP-WSI Test Case 016' along with the data location (Brown et al. 2023) and cite Brown et al. 2022 as the source of this data (see full citations in the 'Relevant References' section below).

Relevant References

S.A. Brown, N. Xie, M.R. Hann and D.M. Greaves (2022). “Investigation of wave-driven hydroelastic interactions using numerical and physical modelling approaches”, Applied Ocean Research, 129, 103363, https://doi.org/10.1016/j.apor.2022.103363.

S.A. Brown, N. Xie, M.R. Hann and D.M. Greaves (2023). “L&R physical modelling data: Regular wave interaction with elastic floating structures (CCP-WSI Test Case 016 Dataset)”, University of Plymouth Research Repository, https://doi.org/10.24382/kre8-ct47.

Resources

Accompanying documents (available at Brown et al. 2023): 

filename

Description

L&R_ElasticStructureA.txt

 

Surface elevation and deflection time-series data for Structure A; tab-delimited text file (lines 1 and 2 - header; column 1 – Time (s); columns 2-5 – surface elevation at wave gauges WG1-WG4 [mm]; columns 6-23 – deflection at Marker 1-9 [mm] (even columns: x deflection; odd columns: z deflection) 

L&R_ElasticStructureB.txt

 

Surface elevation and deflection time-series data for Structure B; tab-delimited text file (lines 1 and 2 - header; column 1 – Time (s); columns 2-5 – surface elevation at wave gauges WG1-WG4 [mm]; columns 6-15 – deflection at Marker 1-5 [mm] (even columns: x deflection; odd columns: z deflection) 

L&R_ElasticStructureC.txt

 

Surface elevation and deflection time-series data for Structure C; tab-delimited text file (lines 1 and 2 - header; column 1 – Time (s); columns 2-5 – surface elevation at wave gauges WG1-WG4 [mm]; columns 6-23 – deflection at Marker 1-9 [mm] (even columns: x deflection; odd columns: z deflection) 

L&R_ElasticStructureD.txt

 

Surface elevation and deflection time-series data for Structure D; tab-delimited text file (lines 1 and 2 - header; column 1 – Time (s); columns 2-5 – surface elevation at wave gauges WG1-WG4 [mm]; columns 6-23 – deflection at Marker 1-9 [mm] (even columns: x deflection; odd columns: z deflection)